Indexable inserts, formed from a hardened material are used in conjunction with cutting tools in milling operations when machining cast iron, aluminum or steel parts. To provide for smooth, high quality cutting profiles, finishing inserts have been developed which have elliptical cutting edges. An elliptical cutting edge allows for the removal of an extremely thin, tapered chip of metal leaving a cut surface which is rounded and smoothed. Typical examples of the finishing inserts found in the prior art are disclosed in U.S. Pat. No. 3,279,034, issued on Oct. 18, 1966 to Kaiser for an "Indexable Cutting Blade"; U.S. Pat. No. 3,434,190, issued on Mar. 25, 1969 to Kaiser, for an "Indexable Cutting Blade"; and U.S. Pat. No. 3,762,005, issued on Oct. 2, 1973 to Erkfritz, for an "Indexable Cutting Insert". These patents disclose indexable inserts, having a cutting edge which is elliptically curved. More specifically, the patents to Kaiser disclose finishing inserts where the rake faces of the inserts are altered to provide a curved cutting edge. The earlier patent to Kaiser alters the front rake face of the insert by curving its outer edges to conform to the surface of an imaginary sphere. The latter Kaiser patent discloses an insert wherein the rake face is grooved to define a curved cutting edge. Similarly, the patent to Erkfritz discloses a finishing insert having grooves undercut along the length of each rake surface.
The indexable inserts disclosed in the prior art were useful in providing finishing type cuts in a workpiece when used in conjunction with a milling tool. However, the changes necessary to alter a standard insert to an elliptical finishing insert resulted in the reduction of the integrity of the rake face of the insert. More particularly, the rounding of the rake face of the insert, or the addition of grooves thereto, for defining the elliptical cutting edges of the insert, effectively reduced the thickness of the insert thereby resulting in a loss of structural strength along the cutting edges. These changes also effectively reduced the surface area of the locating lands which were provided on the edge faces of the inserts. The locating lands were provided to facilitate clamping of the insert within the pocket of a cutter body and serve to locate the inserts in a precise position relative to the body thereby creating the desired axial and radial rake angles.
In addition to the above shortcomings of the prior art systems, it is noted that when these prior art inserts having modifications designed to produce elliptical cutting edges were inserted into a pocket of a milling cutter, the effective geometry of the pocket was altered such that the desired rake angle was not achieved.
Accordingly, it is an object of the subject invention to provide an indexable finishing insert including planar front and rear rake surfaces which provide for the improved structural integrity of the insert.
It is a further object of the subject invention to provide an indexable finishing insert wherein each edge face thereof includes a planar locating land to facilitate the mounting of the insert in the pocket of the cutter body.
It is another object of the subject invention to provide an indexable finishing insert having improved rake face and locater integrity, and in addition, does not alter the rake geometry inherently built into the insert pockets of milling cutters.
It is still a further object of the subject invention to provide an indexable finishing insert having either a positive or a negative geometry.